The present invention relates, in general, to opacity monitors for monitoring the amount of light passing through a gas, in particular for determining how much smoke is being emitted from a stack, and in particular to a new and useful filter cleaning system for such opacity monitors
Monitors are known for measuring how much light is blocked by gases passing through a conduit or stack. A light source and a light sensor lie on opposite sides of an optical path through the conduit or stack. This measurement of opacity for the gases is a measurement of the amount of particles or smoke in the gas.
Part of the optical path between the light source and light sensor is shielded by a pipe to avoid contamination of optic windows separating the light source and sensor from the contaminating environment of the conduit or stack. It is known to supply purging air to the pipes for keeping the optical windows clean and free of soiling or abrasion by particles in the conduit or stack being monitored. Such damage or contamination to the optical windows would produce false opacity readings.
It is known to first filter the purging air through two- and three- stage filters. These filters must frequently be cleaned and changed manually.